1. Field of the Invention
The present invention relates to artificial heart valves and, more particularly, to an improved artificial heart valve made by a vacuum forming technique.
2. The Prior Art
There have been many artificial heart valves developed over the years but none has proved entirely satisfactory. Mechanical valves, such as ball valves, disc valves, hinged valves, etc., are subject to wear and tear and ultimate failure; in addition, in some cases their physical parameters, such as size, shape, flow characteristics, etc., prove unsatisfactory for long term use in the intended environment.
Leaflet valves have appeared to present much promise to prior art experimenters, primarily because leaflet valves closely resemble the actual valving mechanism in natural heart valves. Leaflet valves include flaps or leaflets which project from a frame to cover the framed area. Flow through the frame in one direction causes the leaflets to freely flex downstream to permit through flow. Flow in the opposite direction is resisted by the leaflets.
To my knowledge, the only leaflet-type artificial heart valves which are commercially available have leaflets made from a material which is of human or animal origin. Examples of these are porcine valves, dura mater valves, fascia lata valves and pericardial valves. Such valves cannot be manufactured on a large scale, both because of limitations on available material, in some cases, and primarily because there are no known mass production techniques which function with animal tissue material.
There have been many experiments conducted with artificial heart leaflet valves made of synthetic material such as Teflon, Dacron and Gore-Tex, none of which have led to a satisfactory result. In addition, there have been attempts at the U.S. National Institute of Health to fabricate leaflet valves by injection molding techniques; this, too, was not satisfactory.
Recently, there has been a report by the Avco-Everett Research Labs entitled "Development of an Electrohydraulic Left Heart System" by Sing et al, May 1981. In this report a tricusp semilunar valve is disclosed as being made by solution casting over a male mold. The leaflets are separated by cutting with a Teflon coated knife. The entire structure is later glued with a polyurethane solution over a smooth mandrel to a blood pump structure on one side or to an outflow tube on the other side. This process is extremely cumbersome.